Amazon announced today that users in the U.S., U.K. and Germany can start using Amazon Coins, the company’s virtual currency, to pay for goods on sale from its AppStore for Android devices.

The cash substitute was first launched for Kindle Fire users last year, providing an alternative for purchasing apps and making in-app purchases on Amazon’s platform. Users can purchase coins in bundles which allow them to save up to 10% over spending the same amount of cash, and can also earn coins from purchasing certain apps and completing achievements.

The system has some key advantages for Amazon, including locking Android users into its AppStore if they want to use their Coins. What’s more, if someone buys $20 worth of Coins but only spends the equivalent of $10, the rest is pure profit for Amazon.

Amazon is pitching it as a good deal for developers, too. They still get 70 percent of their app’s sales revenue, whether that revenue comes from Coins or regular currency. Because users can earn free Coins, it means that some developers could actually see an increase in sales from people who wouldn’t ordinarily spend money on apps at all.

Amazon has been working to attract developers to its AppStore. Last month, the company launched a re-designed developer portal which includes a system that allows Android developers to instantly test their app’s compatibility with Amazon’s system. In addition, the company also recently allowed creators of HTML5 apps to start charging for their wares on the AppStore. Having consumer and developer buy-in for its AppStore is key for the company if it wants its app marketplace to compete with Google, but it’s doubly important if Amazon launches a rumored Android-based smartphone.

Amazon’s AppStore app can be downloaded here, and instructions on how to update the app to use Coins can be found here.

Blair Hanley Frank is GeekWire's Bay Area Correspondent. He has also worked for Macworld, PCWorld and TechHive. Follow him on Twitter @belril and email him at blair@geekwire.com.